1. Field of the Invention
The present invention relates generally to vibratory finishing machines, and more particularly to a novel and improved bowl-type vibratory finishing machine.
2. Prior Art
Many surface finishing operations such as deburring, burnishing, descaling, cleaning and the like can be conducted expeditiously in a vibratory finishing machine. Such a machine includes a movably mounted receptacle and a drive system for vibrating the receptacle. Workpieces to be finished are loaded into the receptacle together with finishing media. A finishing action is imparted to the workpieces by vibrating the receptacle so that the mixture of workpieces and media is effectively maintained in a fluid or mobile state with smaller components of the mixture dispersed between large components for impact. Impulse forces imparted to the mixture not only cause repeated impacts among its components but also cause the mixture to churn in a predictable manner as a finishing process is carried out.
Two basic types of vibratory finishing machines are in common use. One type employs an elongated, substantially horizontally disposed receptacle which is vibrated by eccentrics rotating about horizontal axes paralleling the length of the receptacle. This first type of machine is known in the art as a "tub-type mchine" or simply "tub machine", and its receptacle is commonly called a "tub". Another type uses a substantially annular receptacle which is vibrated by rotating one or more eccentrics about a vertical "center axis" located centrally of the receptacle when the receptacle is at rest. This latter type of machine is known in the art as a "bowl-type machine" or simply "bowl machine", and its receptacle is commonly called a "bowl". While tub and bowl machines have many similar characteristics, they are sufficiently different in arrangement and operation that one will frequently offer advantages over the other in solving a particular finishing problem. The present invention relates to bowl-type machines.
During operation of a bowl machine, the bowl vibrates in gyratory movements about a node or null point located somewhere along the machine's center axis. This gyratory movement subjects the bowl's contents to a complex of vertical, radial and tangential impulse components which are intended to effect a uniform dispersion of the smaller components of the workpiece and media mixture among the large components of the mixture for impact. The resultant impulses are so oriented and timed as to cause both circumferential precession of the mixture and rotation of the mixture in essentially radiating vertical planes.
Those skilled in the art maintain different and conflicting theories on where the node or null point should be located along the center axis. Some maintain that the node or null point should be located within or near a horizontal plane which includes the center of gravity of the bowl's contents. This arrangement effectively minimizes horizontal impulse components imparted to the bowl's contents and maximizes the vertical components. Others maintain that a node or null point location slightly below the bottom of the bowl's chamber is desirable since it gives something of a mix of vertical, horizontal and tangential components. Still others advocate higher and lower node or null point locations.
Those skilled in the art similarly advance different and conflicting theories on the number of eccentrics which should be used to vibrate the bowl, the locations of the eccentrics, and the relative orientations of the eccentrics where more than one is used. Still other theories obtain on how and where a drive motor should connect with the eccentrics.
Factors such as node or null point location, the number, location and arrangement of eccentrics, and features of the drive motor connection all intertwine to determine such other factors as:
a. the simplicity or complexity of the machine;
b. the ease with which the machine can be serviced and such parts as bearings replaced;
c. the longevity of service which can be expected from the machine;
d. the sensitivity of the machine to different bowl loadings, i.e., whether it can handle a wide range of large and small, heavy and light loads; and
e. the type of vibratory movement which is imparted to the bowl, which, in turn, determines such things as:
i. the type of circulation movement which will be executed by a mixture of media and workpieces in the bowl; PA1 ii. the direction and rate of precession of the mixture; and PA1 iii. the effectiveness of the resulting finishing action in terms of quality and time required to carry it out.
Previous proposals made in an effort to optimize these factors have resulted in machines which are relatively complex and difficult to service. The need for frequent bearing replacement has been a continuing problem, and the construction of many such machines has made bearing replacement difficult. Most bowl machines are quite sensitive to changes in bowl loading and operate effectively only in a relatively narrow loading range.
The invention described in the referenced Bowl Machine Patent addresses the foregoing and other problems of the prior art. It provides a bowl-type machine having a combination of features that are unique to the industry. The machine is of simple, relatively inexpensive construction. It has a relatively simple but rugged base structure, an equally simple and rugged bowl structure, and utilizes highly durable elastomeric mounts to support the bowl structure on the base structure.
A significant feature of the invention described in the Bowl Machine Patent lies in its novel arrangement of elastomeric mounts. Each mount has one portion secured to the base structure and another portion secured to the bowl structure. The one and another portions define an axis for each mount, and the mounts are arranged such that their axes intersect at a common point along the machine's center axis. The machine's drive system is arranged to vibrate the tub about a node or null point which coincides with this common point. The arrangement of mounts assures that forces imposed on the mounts by movements of the bowl structure load the mounts in shear, i.e., in planes normal to their axes. When arranged and loaded in this manner, the mounts tend to resiliently oppose movements of the bowl structure in any mode other than about the desired node or null point. As a result, the machine is found to be substantially less sensitive to variations in receptacle loading than are other, previously proposed bowl-type machines. A single machine can, for example, handle bowl load volumes within as large a range as 2 cubic feet to 6 cubic feet, and is operable to impart a good finishing action to the load anywhere within this very broad range.
Bowl machine proposals prior to the invention described in the referenced Bowl Machine Patent do not address the problem of stabilizing actual node or null point location. It is believed that the tendency of node or null point location to vary with changes in bowl loading explains, at least in part, the difficulty prior proposals have encountered in providing machines that will handle a wide range of bowl loadings. If the actual location of the node or null point about which a bowl structure moves is displaced from the location for which the machine was designed, the machine operates inefficiently, if at all, and causes excessive wearing of drive and suspension system components.